JP2006523487A - Phased array coil with selectable quadrature coupling - Google Patents

Abstract

The magnetic resonance imaging apparatus includes a main magnet (12) that generates a main magnetic field in a test region (14), a plurality of gradient coils (22) that create a magnetic field gradient in the main magnetic field, and an object disposed in the test region. An RF transmission coil that transmits an RF signal to the test region so as to excite magnetic resonance, and an RF reception coil (16) that receives the RF signal from the object. The RF receiver coil has a first loop (101) and a second loop (102), the first and second loops being arranged on substantially the same plane (x-z). Further included is a signal combiner (120) that orthogonally combines the signals received by the first and second loops.

Description

  The present invention relates to magnetic resonance technology. It finds a specific use for medical diagnostic images and is described in that regard. However, it should be understood that the present invention may find further applications in property control inspection, spectroscopy, and the like.

  In modern magnetic resonance imaging (MRI) scanners, the resonance signal is received by placing a linearly polarized radio frequency (RF) coil adjacent to the patient's surface. The linearly polarized coil receives only one component of the magnetic resonance signal, generally either the horizontal or vertical component. In contrast, the magnetic resonance signal emitted from the object is more accurately determined by a vector rotating in one plane, i.e. having two orthogonal components. Thus, a linearly polarized coil receives only one of the two orthogonal components.

  The orthogonal coil has an annularly polarized magnetic field and receives an orthogonal component of the rotation vector. The orthogonal coils can indicate both current distributions created horizontally and vertically. Thus, the quadrature coil extracts twice as many signals from the rotation vector as the linearly polarized coil. This results in a signal-to-noise ratio that is greater by the square root of 2 or about 41%. However, prior art orthogonal coils are typically volume coils rather than surface coils. For example, some volume quadrature coils have two pillow coils that are 90 degrees apart from each other. The portion of the patient that is to be imaged is placed in a volume that is defined inside the pillow coil. Similarly, other coils are used to determine the volume around the circularly polarized region.

  Accordingly, the preference for orthogonal surfaces or planar coils for applications such as spinal cord imaging has been recognized. See, for example, U.S. Pat. A medizadee surface coil has a thin film dielectric sheet having a first or loop coil defined on one surface and a second or Helmholtz coil defined on the opposite side. The first and second coils are symmetrically arranged on a symmetrical axis or plane. The first coil has an associated magnetic field along the y-axis, and the second coil has an associated magnetic field along the x-axis.

  Spatial strength separation is not easily achievable with the coils disclosed in US Pat. No. 4,918,388 having the first and second coils symmetrically arranged on a symmetrical axis or plane. This limits the use of such coils in applications such as SENSE.

  The present invention provides a new and improved RF coil that overcomes the above problems and others.

  Those of ordinary skill in the art will fully appreciate that aspects of the present invention address these and other issues upon reading and understanding the following description.

According to one aspect of the present invention, a magnetic resonance imaging apparatus is provided. The magnetic resonance imaging apparatus includes a main magnet that generates a main magnetic field in a test region, a plurality of gradient coils that create a magnetic field gradient in the main magnetic field, and an RF signal that excites magnetic resonance in an object disposed in the test region. An RF transmitter coil for transmitting an RF signal to the test area, an RF receiver coil having a first loop and a second loop disposed on substantially the same surface, for receiving an RF signal from the object, and an orthogonal mode And a signal combiner for combining signals received by the first and second loops. According to a more limited aspect of the invention, the geometric centers of the first and second loops are They are moved together in a direction perpendicular to the main magnetic field.

  According to a more limited aspect of the present invention, the first and second loops overlap so as to reduce the mutual inductance between the two loops.

  According to a more limited aspect of the invention, the RF signal received by the first and second loops has components in first and second directions, the first and second The direction is perpendicular to the main magnetic field.

  According to a more limited aspect of the invention, the signal combiner is configured to cause the RF signals associated with the first and second loops in the first direction to be 180 degrees out of phase with each other. Combining the signals by adding the signals, the signal combiner combining the RF signals associated with the first and second loops in the second direction by adding the signals that are in phase .

  According to a further limited aspect of the invention, the magnetic resonance imaging apparatus further comprises switching means for switching the signal combiner from a tilt mode to a phased array mode.

  According to a more limited aspect of the invention, the first and second loops have similar shapes to each other.

  According to another aspect of the present invention, a magnetic resonance imaging apparatus is provided. The magnetic resonance imaging apparatus includes a main magnet that generates a main magnetic field in a test region, an RF transmission coil disposed with respect to the test region so as to excite magnetic resonance with a dipole disposed in the test region, and the RF An RF transmitter for driving a transmission coil, an RF reception coil having a plurality of loop coils arranged in non-orthogonal planes and receiving a magnetic resonance signal from the resonating dipole, and an orthogonal coupling mode or a phased array mode And a signal combiner for selectively combining the signals received by the plurality of loop coils.

  According to a more limited aspect of the present invention, the RF receive coil has an n × m array of loop coils extending perpendicular to the main magnetic field and parallel to the main magnetic field.

  According to a more limited aspect of the invention, the plurality of loop coils have similar shapes to each other.

  According to a more limited aspect of the invention, the RF signal received by the plurality of loop coils has components in first and second directions, the first and second directions being It is perpendicular to the main magnetic field.

  According to a more limited aspect of the invention, the signal combiner is configured to phase the RF signals associated with at least the first and second loops of the plurality of loop coils in the first direction relative to each other. Are combined by adding the signals shifted 180 degrees, and the signal combiner combines the RF signals associated with the first and second loops in the second direction with the signals that are in phase. Combine by adding together.

  According to a more limited aspect of the present invention, the magnetic resonance imaging apparatus further comprises switching means for switching the signal coupler from the tilt mode to the phased array mode.

  According to another aspect of the invention, a magnetic resonance RF coil assembly is provided. The RF coil assembly includes a first loop disposed on a first surface, a second loop disposed on a second surface that is non-orthogonal to the first surface, and the first loop And a signal combiner that orthogonally couples the RF signal associated with the RF signal associated with the second loop.

  According to a more limited aspect of the present invention, the first and second loops are disposed adjacent to each other in substantially the same plane.

  According to a more limited aspect of the invention, the RF coil assembly further comprises means for reducing the mutual inductance between the loops.

  According to a more limited aspect of the invention, the first and second loops are both responsive to an RF signal having components in first and second directions, the first and second loops. The directions are orthogonal to each other.

  According to a more limited aspect of the invention, the signal combiner is configured to cause the RF signals associated with the first and second loops in the first direction to be 180 degrees out of phase with each other. Combining the signals by adding the signals, the signal combiner combining the RF signals associated with the first and second loops in the second direction by adding the signals that are in phase .

  According to a more limited aspect of the present invention, the RF coil assembly further comprises switching means for switching the signal coupler from a tilt mode to a phased array mode.

  According to a more limited aspect of the invention, the first and second loops have similar shapes to each other.

  One advantage of the present invention resides in a two-dimensional array having spatial strength identification.

  Another advantage of the present invention is that the coils in the array can be orthogonally coupled.

  Another advantage of the present invention is that the output of the coils in the array can be selectively taken as a phase array.

  Another advantage of the present invention resides in an RF coil structure that facilitates the manufacture of the coil.

  Further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following description of the preferred embodiment.

  The present invention takes the form of various components and component arrangements, and various operational steps and arrangements of operational steps. The drawings are only used to illustrate preferred embodiments and the invention is not limited thereto.

Referring to FIG. 1, an MRI scanner is shown. The main magnetic field control 10 controls the main magnet 12 which is, for example, a superconducting or normal conducting magnet. The main magnet 12 has a desired force (eg 1.5 Tesla) in a test section or region 14 arranged for the purpose of being tested and is controlled to generate a sufficiently uniform and stable main magnetic field B ₀ . As shown, test section 14 takes the form of a cylindrical hole, although other shapes such as open field test sections are contemplated. Usually, B ₀ is made in the direction of the z axis, which is the central vertical axis of the test section 14.

  The pulse sequence is stored in the sequence memory 32 and executed by the sequence control 30. The sequence control 30 controls the gradient pulse amplifier 20 and the first and second RF transmitters 24 and 25 as necessary. More specifically, the sequence control 30 generates a MR signal that is finally received and sampled, and generates a plurality of MRI pulse sequences for gradient encoding (ie, slice, phase and / or frequency encoding). The gradient pulse amplifier 20 and the transmitter are controlled to make.

The gradient pulse amplifier 20 applies a current pulse to the selected gradient coil 22 so as to create a magnetic field gradient along an axis orthogonal to the test region 14. These magnetic fields spread well in the same direction as B ₀ but have gradients in the x, y and / or z directions, respectively.

The digital radio frequency transmitter 24 transmits radio frequency pulses or pulse packets to a first RF coil 26, such as a whole body birdcage RF coil, so as to transmit RF pulses to the test region. A typical radio frequency pulse is composed of packets of immediately adjacent pulse intervals that have a short period of time required together, and any applied gradients achieve the selected magnetic resonance operation. These RF pulses create a magnetic field B ₁ in the test section 14 at a Larmor frequency determined by the strength of the magnetic field and the geometric constant of the type of magnetic dipole of interest. Typically, this frequency is about 63.8 MHz for a magnetic field having a strength of 1.5 Tesla. The RF pulse is used to saturate, excite the resonance, reverse the magnetism, refocus the resonance, or manipulate the resonance in a selected portion of the test area. 16 is placed in the test area and is optionally controlled by the second RF transmitter 25 to selectively produce an RF signal in the test area 14. As shown in FIG. 1, the second RF coil 16 is a surface coil arrangement. Like the first RF coil 26, these RF pulses, making field B ₁ in the test interval.

  Despite the use of an RF transmitter, a typical RF pulse consists of a packet of adjacent pulse segments with a short period of time required together, and any added tilt will cause a selected magnetic resonance operation. Achieve. An optionally used MRI pulse sequence generates either two-dimensional (2D) or three-dimensional (3D) MR signals. The optionally used MRI pulse sequence comprises some of a plurality of single-echo or multi-echo imaging sequences. Imaging includes many known MRI techniques such as field echo (FE) imaging, spin echo (SE) imaging, echo planar imaging (EPI), echo volume imaging, gradient and spin echo (GSE) imaging. , Fast spin echo (FSE) imaging, single shot FES imaging, 3D volume FSE imaging, parallel imaging techniques (eg, sensitivity encoding (SENSE), simultaneous acquisition of spatial harmony (SMASH), etc.), and / or Or it may be performed using the same. In the case of 2D imaging, the region of interest displays a 2D cross-sectional slice of the imaged object. In the case of 3D imaging, the region of interest displays the 3D volume of the imaged object.

  A magnetic resonance signal originating from the test area 14 is received by an RF receiver coil located proximate to the test area. The RF receiver coil can optionally be a main RF coil 26 or a local RF coil 16. The first receiver 38 receives the magnetic resonance signal from the entire RF coil 26 and demodulates the signal into a plurality of data strings. If the receiver is analog, the first analog / digital converter 40 converts each data string to digital form. Alternatively, the analog / digital converter is disposed between the radio frequency receiving coil 26 and the digital receiver receiver 38.

  The second receiver 34 receives the magnetic resonance signal from the local RF coil assembly unit 16 and demodulates the signal into a plurality of data strings. If the receiver 34 is analog, a local analog / digital converter 36 converts each data stream from the local receiver to digital form. As before, the analog / digital converter can be in front of the digital receiver. Data strings from the receivers 38 and 34 are arranged in the data memory 42 and stored.

  Alternatively, the local RF coil 16 and the transmit and receive hardware coupled thereto may be just RF transmit / receive hardware in the system.

  It should be understood that the local coil 16 is subdivided into a number of sections or loops, each of which can be connected to the second receiver 34. Thereby, the second receiver 34 may have one of each of a number of receivers and a combined analog / digital converter, for example a local coil 16 section. Alternatively, a single multi-channel receiver can be used. Another embodiment has a single channel receiver that receives the combined signal from the local coil section.

  The data sequence is reconstructed into an image display by a reconstruction processor 50 that applies inverse Fourier variation or other suitable reconstruction algorithm. The image may represent a planar slice of a patient, an array of parallel planar slices, a three-dimensional volume, or the like. Next, electronic image display is a video process that converts a slice, projection, or other part of the image display into an appropriate format for a display device such as a monitor 56 that provides a human-readable composite image display. It is stored in an image memory 52 that is selectively accessed by the device 54.

  Referring to FIG. 2, the local coil assembly unit 16 includes a first loop coil 101 and a second loop coil 102. In one embodiment, the first and second loop coils are substantially placed on the same plane, eg, the xz plane, and overlap to reduce the effect of mutual inductance between the coils. However, it should be understood that in other methods of reducing mutual inductance, such as inductive isolation, the loops do not necessarily overlap. In the example shown, the centers of the coil loops are moved from each other in the x direction. Movement in the z direction is shown for clarity purposes only. As shown in FIG. 2, both loop coils are rectangular, but it should be understood that other shapes of coils are contemplated. Further, it should be understood that the local coil has a prior art conditioning capacitor and transmit separator. These elements are not shown here for simplicity.

  Continuing with FIG. 2, the first loop 101 is electrically connected to the first preamplifier 111. The second loop coil 102 is electrically connected to the second preamplifier 112. Outputs from the first and second preamplifiers 111 and 112 are input to the signal combiner 120. The signal combiner 120 is connected to the second RF receiver 34.

  FIG. 3 shows one embodiment of the signal combiner 120. As can be seen, the signal combiner 120 has a first distributor 131 whose input comes from the first preamplifier 111. The first distributor 131 has two outputs. The first output is connected to the first adder 141, and the second output is connected to the second adder 142. The first adder 141 is connected to the first phase shifter 151. In the embodiment shown, the phase shifter is a 90 degree phase shifter. The first phase shifter 151 is connected to the third adder 143.

  Continuing with FIG. 3, the signal combiner 120 also has a second distributor 132, whose input comes from the second preamplifier 112. The second distributor 132 has two outputs. The first output is connected to the first adder 141, and the second output is connected to the second phase shifter 152. In the embodiment shown, the second phase shifter is a 180 degree phase shifter. The second phase shifter is connected to the second adder 142 and provides an input thereto. Together with the first phase shifter, the output from the second adder 142 is connected to the third adder 143. The output from the third adder 143 is connected to the second RF receiver 34.

  In an alternative embodiment, signal combiner 120 can be a quadrature combiner known as one of the prior art. FIG. 4 shows a circuit diagram of such a quadrature coupler. As known in the prior art, coupling capacitors C1, C2, C3, C4, C5, C6 and inductors L1, L2 make up a quadrature coupler when coupling diodes D1, D2 are biased. When the diode is biased, the local RF coil assembly 16 acts as a coupling coil. When the diode is not biased, capacitors C1, C2 and inductor L1 and capacitors C3, C4 and inductor L2 make a 50 ohm transmission line. In this latter mode of operation, the local RF coil assembly 16 acts as a phased array coil.

In operation, the main magnetic field B ₀ is generated in the test area 14 and the object is placed in it. A series of RF and magnetic field gradient pulses reversal or excite magnetic spins, have magnetic resonance, refocus on magnetic resonance, manipulate magnetic resonance, spatially or magnetically resonate the spin The opposite is encoded and applied to generate an MRI pulse sequence. More specifically, the gradient pulse amplifier 20 applies a current pulse to the selected one or pair of gradient coils 22 to create a magnetic field gradient along the x, y and z axes of the test region 14. The entire RF transmitter 24 drives the entire transmit coil 26 to transmit RF pulses or pulse packets to the test region 14. Alternatively, similarly, the local RF coil transmitter 25 drives the local RF coil 16 to transmit an RF pulse or pulse packet to the test region 14.

  Regardless of the MRI pulse sequence or technique used, sequence control 30 adjusts a plurality of MRI pulse sequences that generate MR signals that are ultimately received from the test region. For the selected sequence, each echo of the received MR signal is received by the first RF coil 26 or the local RF coil 16.

  When the local RF coil 16 is operative to receive signals from the test area, the local coil can operate in two modes of operation. In the first mode, the local RF coil 16 acts as a quadrature coil. Referring to the embodiment shown in FIGS. 2 and 3, RF signals received by the first and second loop coils 101, 102 from the test region are transmitted to the first and second preamplifiers 111, 112, respectively. And amplified for further processing.

  Next, the amplified signal is transmitted to a signal combiner 120 where RF signals in the vertical mode (y direction) and the horizontal mode (x direction) are orthogonally coupled. Generally speaking, referring to FIG. 5, the sensitivity of each loop 101, 102 has components in the x and y directions. Referring to FIG. 5, for the sake of clarity, the loops 101, 102 are shown in cross section without any overlap. The vertical mode Y is obtained by adding the preamplifier outputs of the first and second preamplifiers that are in phase. The horizontal mode X is obtained by adding the preamplifier output from the first loop 101 to the preamplifier output of the second loop 102 that is 180 degrees out of phase.

More specifically, referring again to FIG. 3, the vertical mode Y is, RF signals from the first preamplifier 111 (S _A), RF signal (S _B) of the signal from the second preamplifier 112 Obtained by transmitting to the combiner 120. The RF signals S _A and S _B are distributed by the first and second distributors 131 and 132, respectively. As known in the prior art, this gives two output signals from each distributor equal to 0.7 S _A for the first distributor and 0.7 S _B for the second distributor. Bring.

To obtain the vertical mode, the first output from each distributor is added in phase by a first adder 141. This results in a signal S _Y equal to 0.7S _A + 0.7S _B.

To obtain the horizontal mode, the second output from the second distributor 132 is phase shifted by the second phase shifter 152. In the example shown, the phase shift is 180 degrees. Therefore, the second phase shifter 152 outputs a signal equal to -0.7S _B. This signal is then added to the second output of the first distributor 131 by the second adder 142. This results in a signal S _X equal to 0.7S _A −0.7S _B.

In order to combine the horizontal and vertical signals S _X , S _Y that are in quadrature, the vertical signal S _Y is phase shifted by the first phase shifter 151. In the example shown, S _Y is phase shifted by 90 degrees. This results in a signal equal to j (0.7S _A + 0.7S _B ). This signal is added to the horizontal signal S _X by the third adder 143. This is a signal like
S _QUAD = (0.7S _A -0.7S _B ) + j (0.7S _A + 0.7S _B ) (1)
Bring. This is as follows:
S _QUAD = S _A (45 degrees) + S _B (135 degrees) (2)
Can be rewritten.

In the example shown, the S _B component is delayed by 90 degrees from the S _A component, so a standard quadrature combiner can be implemented as a signal combiner, as shown schematically in FIG.

  As described above, the local RF coil 16 can operate in two modes of operation. In the first mode, the local RF coil 16 acts as a direct coil. In the second mode of operation, the local coil acts as a phased array coil. In this mode of operation, the signal combiner 120 is switched so that two separate signals corresponding to the first and second loop coils 101, 102 are transmitted separately to the respective receiving channels. One such embodiment enables parallel processing applications such as SENSE.

  In the phased array embodiment, the combining circuit shown in FIG. 4 may be used as the signal combiner 120. Here, the quadrature coupler is switched on or off according to the DC bias present at the second port J2. If phase alignment mode is desired, a positive bias is applied. PIN diodes D1 and D2 are switched off and the first and second loop signals are valid at the first and second ports J1 and J2. If a quadrature coupler is desired, a negative bias is applied to the second port J2. This produces an orthogonal signal at one of the ports J1 or J2 depending on the magnetic field direction. Non-orthogonal signals are present at other ports.

  Despite the coil acting as an RF receiver coil or the local coil assembly 16 operating, the received MR signal is received by the combined RF receiver 38, 34 and analog / digital converters 40, 36. Time is sampled to produce a sequence or array of data at the sampled data points representing each echo. This raw MR data is then captured into the MR data memory or buffer 42. The MR data memory corresponds to a data matrix commonly known as k-space. Based on the specific gradient coding given to each echo, the corresponding MR data is mapped or assigned to an arrangement in k-space.

  The data is reconstructed into an image display by a reconstruction processor 50 that applies an inverse Fourier transform or other suitable reconstruction algorithm. The electronic image display is then stored in the image memory 52. The image memory converts slices, projections, or other parts of the image display into the appropriate format for a display device such as a monitor 56 that provides a human-readable composite image display of the composite image. Is selectively accessed by the video processing device 54.

  The coil 16 has been described based on one embodiment having two loop coils. However, various sized arrays are contemplated. For example, it is possible to have a spinal coil with two longitudinal five-connected loops arranged side by side, such as an array of 2 × 5 coils extending longitudinally in the z direction. In such an embodiment, the loop arrangements overlap to provide separability for each pair. Diagonal neighbor separation is achieved by capacitive cancellation with a common diagonal conductor. The next closest separability is unique from individual to individual. Referring to the spinal cord array example, each face of the spinal coil has two loops where the preamplifier output can be taken separately as described above or in quadrature coupling.

  In another embodiment, the local coil has an n × m array where n is a multiple of 2 in the x direction and m is the z direction (or magnetic field direction). Such an array can be orthogonally coupled to a nm / 2 signal.

  In yet another embodiment, the first, second, third and fourth loop coils 201, 201, 203 and 204 are spaced around the test area as shown in FIG. The These coils are separated from each other using known separation techniques. In this embodiment, the coils can be selectively coupled for sensitivity encoding along the horizontal direction (x direction) or in the vertical direction (y direction).

  For sensitivity encoding in the x direction, the first and second loop coils 201, 202 can be orthogonally coupled and the third and fourth loop coils 203, 204 can be orthogonally coupled. This results in a pair of orthogonal coils having sensitivity encoding capability in the x direction as shown in FIG. For sensitivity encoding in the y direction, the second and third coils can be orthogonally coupled and the first and fourth coils can be orthogonally coupled. This results in a pair of orthogonal coils having sensitivity encoding capability in the y direction as shown in FIG.

  FIG. 7 shows how the structure of the coil shown in FIG. 6 can be selectively used as a phased array coil with four coils connected vertically or as a pair of orthogonal coils as described above. More specifically, FIG. 7 shows a selectable quadrature combination of four channels in which the combination of the first, second, third and fourth coils 201, 202, 203, 204 realizes two quadrature receive channels. Indicates a vessel. The combiner can select spatial discrimination in either the x or y direction as desired.

  In this embodiment, signals are taken from the respective loops 201, 202, 203, 204 and input to the first, second, third and fourth preamplifiers 211, 212, 213, 214, respectively. The amplified signal is input to the signal combiner 230 at the first, second, third and fourth combined inputs 221, 222, 223 and 224. The circuit of the signal combiner 230 shown in FIG. 7 has PIN diode switches D1... D8 that serve to switch the coil between a quadrature mode and a phased array mode. Capacitors C1 ... C16 and inductors L1 ... L4 form a quadrature coupler. Inductors L5... L14 function as direct current bypass inductors, and resistors R1... R8 are current limiting resistors for switching bias.

By placing a negative DC bias on ports J2 and J4, PIN diodes D1, D3, D5 and D7 are biased. This serves to orthogonally couple the first and second loop coils and the third and fourth loop coils for spatial discrimination in the x direction. The quadrature signal appears at ports J1 and J3 or J2 and J4 according to the B ₀ magnetic field polarity.

  By placing a positive bias on ports J2 and J4, PIN diodes D2, D4, D6 and D8 are biased. This serves to orthogonally couple the first and fourth coils and the second and fourth coils for spatial discrimination in the y direction.

  By placing a zero voltage DC bias on J2 and J4, all PIN diodes are turned off. In this case, quadrature coupling does not occur and separate phased array signals can be taken from all four coils.

  The invention has been described with reference to the preferred embodiments. Obviously, changes and exchanges can be made by others upon reading and understanding the foregoing. It is noted that the invention is to be construed as having all such modifications and alterations as they are within the scope of the appended claims or equivalent description.

1 is a diagram of a magnetic resonance imaging apparatus according to the present invention. It is a figure of the local RF coil assembly part which has two loop coils. It is a figure of a signal coupler. It is a circuit diagram of an orthogonal coupler. It is a figure of the magnetic field detection sensitivity pattern of two coils shown by the cross section. It is a figure which shows the coil arrangement | sequence arrange | positioned at intervals around the test area | region. It is a circuit diagram of the orthogonal coupler which can select four channels.

Claims (20)

A main magnet that generates a main magnetic field in the test area;
A plurality of gradient coils for creating a magnetic field gradient in the main magnetic field;
An RF transmitter coil that transmits an RF signal to the test area to excite magnetic resonance in an object disposed in the test area;
An RF receiver coil having a first loop and a second loop arranged in substantially similar planes and receiving an RF signal from the object;
And a signal combiner for combining signals received by the first and second loops in orthogonal mode.   The magnetic resonance imaging apparatus of claim 1, wherein the geometric centers of the first and second loops are moved relative to each other in a direction perpendicular to the main magnetic field.   3. The magnetic resonance imaging apparatus according to claim 2, wherein the first and second loops overlap each other so as to reduce a mutual inductance between the both loops.   The RF signal received by the first and second loops has components in first and second directions, the first and second directions being perpendicular to the main magnetic field. The magnetic resonance imaging apparatus according to claim 1, wherein:   The signal combiner combines the RF signals associated with the first and second loops in the first direction by adding the signals that are 180 degrees out of phase with each other; 5. The magnetic device of claim 4, wherein said device combines said RF signals associated with said first and second loops in said second direction by adding said signals that are in phase. Resonance imaging device.   2. The magnetic resonance imaging apparatus according to claim 1, further comprising switching means for switching the signal coupler from a tilt mode to a phased array mode.   2. The magnetic resonance imaging apparatus according to claim 1, wherein the first and second loops have shapes similar to each other. A main magnet that generates a main magnetic field in the test area;
An RF transmitter coil positioned with respect to the test area to excite magnetic resonance with a dipole disposed in the test area;
An RF transmitter for driving the RF transmission coil;
An RF receiver coil having a plurality of loop coils arranged in non-orthogonal planes and receiving a magnetic resonance signal from the resonating dipole;
A magnetic resonance imaging apparatus comprising: a signal combiner that selectively combines the signals received by the plurality of loop coils in an orthogonal coupling mode or a phased array mode.   9. The magnetic resonance imaging apparatus according to claim 8, wherein the RF receiving coil has an n × m array of loop coils extending perpendicularly to the main magnetic field and parallel to the main magnetic field. .   9. The magnetic resonance imaging apparatus according to claim 8, wherein the plurality of loop coils have shapes similar to each other.   The RF signal received by the plurality of loop coils has components in first and second directions, and the first and second directions are perpendicular to the main magnetic field. The magnetic resonance imaging apparatus according to claim 8.   The signal combiner adds the RF signals associated with at least the first and second loops of the plurality of loop coils in the first direction to the signals that are 180 degrees out of phase with each other. And the signal combiner combines the RF signals associated with the first and second loops in the second direction by adding the signals that are in phase. The magnetic resonance imaging apparatus according to claim 11.   9. The magnetic resonance imaging apparatus according to claim 8, further comprising switching means for switching the signal coupler from a tilt mode to a phased array mode. A first loop disposed on a first surface;
A second loop disposed on a second surface that is non-orthogonal to the first surface;
A magnetic resonance RF coil assembly comprising a signal combiner for orthogonally coupling an RF signal associated with the first loop with an RF signal associated with the second loop.   The magnetic resonance RF coil assembly of claim 14, wherein the first and second loops are disposed adjacent to each other in substantially the same plane.   16. The magnetic resonance RF coil assembly of claim 15, further comprising means for reducing mutual inductance between the loops.   Both the first and second loops are responsive to RF signals having components in first and second directions, the first and second directions being orthogonal to each other, The magnetic resonance RF coil assembly according to claim 14.   The signal combiner combines the RF signals associated with the first and second loops in the first direction by adding the signals that are 180 degrees out of phase with each other; 18. The magnetic device of claim 17, wherein the device combines the RF signals associated with the first and second loops in the second direction by adding the signals that are in phase. Resonant RF coil assembly.   15. The magnetic resonance RF coil assembly according to claim 14, further comprising switching means for switching the signal coupler from a tilt mode to a phased array mode.   15. The magnetic resonance imaging apparatus according to claim 14, wherein the first and second loops have shapes similar to each other.

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